Before the big bang Time did not exist, nor mass, nor energy, nor velocity.

Or did they?

Thanks you for your help.

I think most professional astronomers would be surprised if it turned out that the Big Bang actually turned out to be a singularity, a place where time evolution terminates.

We don't know. The main prevailing mathematical model breaks down as it approaches the presumed start of expansion. But there are other newer models which do not break down, and they continue on back in time.

If these models are right, then there is time and ordinary space, matter, energy back before expansion started. The question is, which models are right.

Their stuff is written by physicists, often ones whose research is in the relevant area, but it is public-outreach non-technical style, so easier to understand. Try reading the short essay called "A Tale of Two Big Bangs". Here's an exerpt:

"...Whether or not there really was a big bang singularity is a totally different question. Most cosmologists would be very surprised if it turned out that our universe really did have an infinitely dense, infinitely hot, infinitely curved beginning. Commonly, the fact that a model predicts infinite values for some physical quantity indicates that the model is too simple and fails to include some crucial aspect of the real world. In fact, we already know what the usual cosmological models fail to include..."

I guess the point is that as of today there is no scientific reason to suppose that time stops at the BB, or that there is no time-evolution. One model breaks, other models don't, and so far there is no scientific reason to prefer one over the other. There have to be observations to check predictions.

There was an older view that was widespread before 2005 that there is no time before BB, that the idea was "meaningless". But that idea is old-fashioned now. You get it mainly from amateurs. Roger Penrose noted the change in a talk he gave in 2005 at Cambridge Isaac Newton Center.

I think most astronomers would be surprised if it turned out that the Big Bang actually turned out to be a singularity, a place where time evolution terminates.

We don't know. The main prevailing mathematical model breaks down as it approaches the presumed start of expansion. But there are other newer models which do not break down, and they continue on back in time.

If these models are right, then there is time and ordinary space, matter, energy back before expansion started. The question is, which models are right.

I don't know about those. I stick to pretty conventional mainstream stuff. We'd probably better not get into those incredible theories because this Forum is really not for highly speculative notions, it is more aimed at understanding and discussing the models that the bulk of professional researchers work on. The stuff they have conferences and present papers about.